* {
  margin: 0;
  padding: 0;
}

ul,
li,
ol {
  list-style: none;
}
header {
  height: 40px;
  background-color: rgb(20, 20, 20);
  margin-bottom: 10px;
}
header ul {
  width: 1000px;
  margin: 0 auto;
  height: 40px;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
header ul ol {
  display: flex;
  height: 100%;
  justify-content: flex-end;
  align-items: center;
}
header ul li {
  line-height: 40px;
  height: 100%;
  width: 100px;
  margin-right: 50px;
}
header a {
  text-decoration: none;
  text-align: center;
  display: block;
  width: 100%;
  height: 100%;
  color: #fff;
}
header a:hover {
  color: #fff;
  background-color: #333;
}
